I recently build the Son of Fermentation Chiller and noticed that my fan seems to make a high pitched whine when it's not running. The components I've purchased are:
12 volt DC Computer Fan (Radio Shack model 273-243B)
Enercell AC Adapter 1.5 12 volt (Radio Shack model 273-315)
Honeywell Thermostat from Home Depot (Model # CT31A)
I've connected everything as the original Son of Fermentation Chiller guide recommended. Fan Negative (Blue) to Adapter Negative (Written Wire), Fan Positive (Red) to Thermostat G, and Adapter Positive (Blank Wire) to Thermostat R.
The circuit works exactly as intended. When the thermostat is set to On the fan runs continuously. When set to Auto the fan turns on when the ambient temperature is above the thermostat's setting. The Adapter is set to 12 volts and the thermostat is set to Cool.
Whenever the thermostat is set to auto and the temperature is below the thermostat's setting (Fan is not running) I hear a very high pitched whine or squeal coming from the circuit. I believe it's coming from the fan though I'm not entirely sure. This happens immediately when the adapter is plugged in and the thermostat is set to a very low temperature. When either I switch the thermostat to On then back to Auto, or when the thermostat is on Auto and I raise the temperature setting then lower it again, either way turning the fan On then Off again essentially, the whine takes about 1 second to build then settles into the familiar high pitched noise again. I heard nothing with the thermostat set to Off.
Does anyone have experience with these components, or circuits in general? Any ideas on what could be causing the whine? More importantly, is it anything to worry about? I'm cautious to utilize the electronics until I understand what's causing the noise. Any help is appreciated. Thank you.